In the related art, a fan control apparatus for controlling an in-vehicle heat-exchanger cooling fan is put under the control of a vehicle ECU (Electronic Control Unit), and, in control of the cooling fan, the motor rotation speed is controlled based on the duty ratio of a PWM (pulse width moduration) signal output from the vehicle ECU.
The motor rotation speed is controlled based on a vehicle speed, an engine coolant temperature, and an AC pressure. While the air conditioner is on, an air-conditioner ECU calculates the necessary fan control based on a pressure signal for the air conditioner and a vehicle-speed signal received from the vehicle and outputs the result as a signal to the vehicle ECU. The vehicle ECU adds, to that signal, the vehicle speed and the engine coolant temperature to determine the rotation speed of a fan motor and outputs a fan-driving PWM signal. On the other hand, while the air conditioner is off, the vehicle ECU determines the fan rotation speed based on the vehicle speed and the engine coolant temperature and outputs a fan-driving PWM signal.